U.S. Pat. No. 5,896,669 discloses a tank for an operating substance for a portable handheld work apparatus, namely, for an overhead branch cutter. The tank is configured as one part and has a fill opening for filling with lubricating oil as well as a suction connection for supplying the lubricating oil to a saw chain running on a guide bar.
The tank containing the operating substance is fixed on an attachment flange for the guide bar. During operation, external mechanical forces operate on the tank. Furthermore, an underpressure can occur for an operating substance tank as the tank empties and this underpressure hinders the dispensing of the lubricating oil.
It is an object of the invention to improve an operating substance tank in such a manner that an increased buildup of underpressure in the tank is prevented with a simple configuration.
The tank of the invention for holding an operating substance includes: a tank housing having a tank interior and including a first housing part; and, a second housing part connected to the first housing part and defining the tank interior conjointly therewith; a valve unit disposed in the tank interior and including a valve member and a valve opening; the second housing part defining the valve opening; the first housing part including the valve member arranged therein so as to be in seal-tight contact engagement with the valve opening; and, the tank including a fill opening and a suction connection through which the operating substance is drawn.
A simple mounting of an aerating valve is possible with the formation of the operating substance tank from two housing parts. The valve member is held by the first housing part of the tank housing and this valve element comes to lie seal tight against a valve opening of a through bore on the second housing part when joining the two housing parts of the operating substance tank. Advantageously, the valve member is held on a stub which projects from the first housing part in the direction toward the second housing part. The stub is preferably of a cylindrical shape. The valve member can be configured as a cylindrical stub which, with its flat end face, lies in surface contact on the opening and around the opening of the passthrough bore on the second housing part. The effective sealing surface has the form of an annular disc. An excellent resistance against dirt particles is provided by this large area sealing surface. The valve member can be provided as a sealing cone whereby a linear-shaped to a ring-shaped sealing surface is formed. During operation of a portable handheld work apparatus, the aerating valve functions to compensate the underpressure which develops as the operating substance tank becomes empty. The valve opens to the ambient and thereby permits the pressure equalization.
When the underpressure develops in the tank as the operating substance is drawn therefrom via the suction connection, the ambient atmospheric pressure operates on the valve member made, for example, of an elastomeric sealing mass and causes at least a portion thereof to lift away from the valve opening to allow air to flow into the tank to compensate for the underpressure thereby ensuring that the operating substance continues to flow out through the suction connection.
It is practical to configure the valve member from an elastomeric material, preferably, from a two-component sealing mass which is sprayed onto the first housing part and sets. The valve member can also be configured as a cylindrically-shaped full rubber part. This full rubber part is connected on its one end to the cylindrically-shaped stub on the first housing part and lies seal tight on the valve opening of a through bore to the atmosphere on the second housing part with a planar sealing surface configured transversely to the longitudinal axis of the valve member.
An intermediate layer of a solid seal, preferably an elastomeric two-component sealing mass, is provided between the tank surfaces of the housing parts for sealingly connecting the two housing parts of the tank housing. Preferably, in advance of connecting the housing parts, a two-component sealing mass is sprayed onto the flange-like partition surfaces of a housing part and, after hardening or setting of the two-component sealing mass, the housing parts are connected to each other via a form-tight, force-tight or material-tight connection.
If the tank for the operating substance is used in a portable handheld work apparatus, then it is practical to configure one housing part of the tank housing of the operating substance tank (preferably the second housing part having the valve opening of the through bore) with the apparatus housing of the portable handheld work apparatus itself. If the work apparatus is an overhead branch cutter and if the operating substance tank functions to store lubricating oil for a saw chain, then it is practical to utilize an attachment flange of the guide bar as the second housing part of the tank housing of the operating substance tank and to arrange the operating substance tank on the side of the attachment flange lying opposite to the work tool, especially the guide bar having the saw chain running along the periphery thereof.
The leakage oil, which runs through the through bore of the valve during operation of the operating substance tank on the overhead branch cutter, can be directed to an intended use. For this purpose, it is practical to so arrange the through bore on the second housing part (that is, on the attachment flange of the overhead branch cutter) that this through bore opens on the side of the attachment flange (the side lying opposite to the tank housing) on the work tool, especially in the slide region of the moving saw chain. To effect a simple and wear-resistant assembly of the operating substance tank, it is practical to make the tank housing of plastic (preferably of fiber-reinforced plastic) with a local wall thickness, which varies over the periphery of the tank housing, in order to configure those wall regions to have greater strength which are especially subjected to mechanical loads.